The automatic verification of a signature is a useful way to identify a human being for purposes, e.g., of establishing his authority to complete an automated transaction, or gain control of a computer, or gain physical entry to a protected area. Signatures are particularly useful for identification because each person's signature is highly unique, especially if the dynamic properties of the signature are considered in addition to the shape of the signature. Dynamic properties include stylus pressure and velocity as functions of time. Even if a skilled forger can accurately reproduce the shape of a signature, it is unlikely that he can reproduce the dynamic properties as well.
Numerous practitioners have addressed the problem of signature verification. For example, verification methods that involve analyzing the shape of the signature are described in U.S. Pat. No. 4,985,928, issued to R. K. Campbell, et al. on Jan. 15, 1991, U.S. Pat. No. 4,972,496, issued to R. Sklarew on Nov. 20, 1990, and U.S. Pat. No. 4,454,610, issued to G. C. Sziklai on Jun. 12, 1984.
Other practitioners have addressed the dynamic properties of the signature. For example, U.S. Pat. No. 4,128,829, issued to N. M. Herbst, et al. on Dec. 5, 1978, discloses a verification method based on the acceleration and pressure signals from the signature. U.S. Pat. No. 4,901,358, issued to L. Bechet on Feb. 13, 1990, discloses a verification method based on the x and y speed signals of the signature. U.S. Pat. No. 4,024,500, issued to N. M. Herbst, et al. on May 17, 1977, discloses the use of the speed signal to separate the signature into segments, followed by shape analysis of the segments.
The use of the speed signal for segmentation, as disclosed, for example, in the Herbst '500 patent discussed above, leads to efficient shape analysis. It is also apparent from the above-cited patents that pattern matching based on the speed signal or other dynamic properties is independently useful for signature verification. By combining pattern matching based on shape analysis with such matching based on dynamic properties, signature verification could, in principle, be made more reliable. However, practitioners in the art have hitherto failed to provide a verification method which uses dynamic properties to segment the signature, performs shape analysis on the resulting segmented signature, and again uses dynamic properties for dynamic pattern-matching.